Management of Second-Degree Heart Block
For patients with second-degree heart block, management should be based on the type of block, presence of symptoms, and hemodynamic stability, with permanent pacing recommended for symptomatic patients or those with Mobitz type II block regardless of symptoms. 1
Initial Assessment and Classification
- Second-degree AV block is characterized by intermittent failure of atrial impulses to conduct to the ventricles and is classified into two main types 2, 3:
- Mobitz type I (Wenckebach): Progressive PR prolongation before blocked beat; usually occurs at AV node level
- Mobitz type II: Constant PR intervals before and after blocked beats; usually occurs below the AV node in the His-Purkinje system
Acute Management
Reversible Causes
- Patients with transient or reversible causes (e.g., Lyme carditis, drug toxicity) should receive medical therapy and supportive care, including temporary pacing if necessary, before determining need for permanent pacing 1
- For patients on chronic stable doses of medically necessary beta-blockers or antiarrhythmics with symptomatic second-degree block, it's reasonable to proceed directly to permanent pacing 1
Medical Therapy for Symptomatic Patients
For AV nodal block with symptoms or hemodynamic compromise:
For symptomatic patients with low likelihood of coronary ischemia:
- Beta-adrenergic agonists (isoproterenol, dopamine, dobutamine, epinephrine) may be considered to improve conduction and heart rate 1
For blocks associated with acute inferior MI:
- Intravenous aminophylline may be considered to improve AV conduction 1
Temporary Pacing
- For symptomatic second-degree block refractory to medical therapy, temporary transvenous pacing is reasonable 1
- For prolonged temporary pacing, externalized permanent active fixation leads are preferable to standard passive fixation temporary leads 1
- Temporary transcutaneous pacing may be considered for hemodynamic compromise refractory to medical therapy until transvenous or permanent pacing is established 1
Chronic Management and Permanent Pacing Indications
Definite Indications for Permanent Pacing
- Mobitz type II second-degree AV block: Permanent pacing recommended regardless of symptoms 1
- Symptomatic second-degree AV block: Permanent pacing recommended regardless of type 1
- Symptomatic AV block due to reversible cause that doesn't resolve despite treatment: Permanent pacing recommended 1
Other Indications Based on Specific Conditions
- Neuromuscular diseases with second-degree AV block: Permanent pacing recommended (with defibrillator capability if needed) 1
- Cardiac sarcoidosis or amyloidosis with second-degree AV block: Permanent pacing reasonable (with defibrillator capability if needed) 1
- Symptomatic marked first-degree or Mobitz type I block: Permanent pacing reasonable when symptoms clearly attributable to AV block 1
Contraindications to Permanent Pacing
- Asymptomatic vagally mediated AV block 1
- Complete resolution of AV block after treatment of a reversible and non-recurrent cause 1
Additional Testing for Chronic Management
- For patients with symptoms of unclear etiology who have first-degree or Mobitz type I block, ambulatory ECG monitoring is reasonable 1
- For patients with exertional symptoms and first-degree or Mobitz type I block at rest, exercise testing is reasonable 1
- In selected patients with second-degree block, electrophysiology studies may be considered to determine the level of block 1
Special Considerations
- Prognosis of untreated Mobitz type I block may not be as benign as traditionally thought; five-year survival rates for untreated Mobitz type I and II blocks are similar 5
- Children with second-degree heart block require close monitoring as 30% may progress to complete heart block or require pacemaker placement 6
- Correct identification of Mobitz type II block is critical as it is invariably at the His-Purkinje level and requires pacemaker implantation 2